Solution polymerization processes are typically carried out at temperatures that are above the melting point of the ethylene interpolymer produced. In a typical solution polymerization process, catalyst components, solvent, monomers and hydrogen are fed under pressure to one or more reactors.
For ethylene homo polymerization, or ethylene copolymerization, reactor temperatures can range from about 80° C. to about 300° C. while pressures generally range from about 3 MPag to about 45 MPag and the ethylene interpolymer produced is dissolved in a solvent. The residence time of the solvent in the reactor is relatively short, for example, from about 1 second to about 20 minutes. The solution process can be operated under a wide range of process conditions that allow the production of a wide variety of ethylene interpolymers. Post reactor, the polymerization reaction is quenched to prevent further polymerization, by adding a catalyst deactivator, and passivated, by adding an acid scavenger. Once passivated, the polymer solution is forwarded to a polymer recovery operation where the ethylene interpolymer is separated from process solvent, unreacted residual ethylene and unreacted optional α-olefin(s).
There is a need to improve the color index of ethylene interpolymer products. The color index of an ethylene interpolymer product is an important attribute; frequently color is often a customer's first impression of product quality, thus it is essential that the color of an ethylene interpolymer meets the customer's expectation. In this disclosure the color index of ethylene interpolymer products was measured according to ASTM E313-10 and quantified using the Whiteness Index (WI) and the Yellowness Index (YI). WI and YI provide numbers that correlate with visual ratings of whiteness and yellowness of samples viewed in daylight by an observer having normal color vision. In this disclosure the WI of ethylene interpolymer ranged from about 10 to about 65; higher WI's are preferred by customers, i.e. more white. The YI of ethylene interpolymer ranged from about 15 to about −4; lower YI's are preferred by customers, i.e., less yellow.